Manufacture of invisible pictures.



UNITED STATES 'E'RNST'KRETSOHMANN, or GROSSILAFFERDE, GERMANY.

MAN UFACTU RE or; INVIS I B 'L-E Ploru R-Es;

srncrrrcnrxon formingpart of Letters Patent no. 634,956, dated mum; 1,1 eo1..

' Application filed June so, 1900. Serial No. 21.013. 11% sp'eohnenml Y *To all whom, it may "concern;-

Be it known that I, ERNST Knnrscnmn, a

' citizen of the Kingdom of Prussia, and a-resident of-Gross Lalferde, Germany, (whose post-' 5 oflice address is 'Gad-enstedterstrasse 256,)

have" invented certain- Q-new'and useful Ini- ,provementsin the Manufacture of Invisible Prints, of which thefollowing is a specifica- :0 V This invention relates toa method of manufact urin g invisible prints which may be made visible byv heating orlother means;

' To produce colorchanging prints, metal and other salts used inthe manufacturing of n pathetic inks are mixed with varnish, just he any ordinary printing-ink. The haloid purpose, their color being a pale rose when 7 cold, but on being heated changing to a deep :0 blue. *Nowa print eifecte'd by aid of a cobalt printing-ink will not be invisible, but its con- 7 tourswill appear plainly visible. on the sur- ..face of thelpap'eri {Toeflfect an absolute invisibility of a cobalt print, a-paper having the 5 color of the print has qjbe'used and the print to be.pi-inted.-upon it;- Thus a pale-rose-paper being printed upon with cobalt ink will show only very faint traces of the print. To

- formed, what I claim issalts of cobalt are espepiallyadapted for this" in presenceof two witn e -1" makethe latter'absolutelyinvisible,the print-- I ing has to be done first with afast'white ink 30'- and then with the rose ,oobalt ink covering,.' the white. While; cobalt salts lend them-' selves especially we'll'ito the productionjloff such like prints, any other sympathetic-i. e..

color-changinge'substance may be used as'f3'5. well, the color of the second (compensating) inklbeing cho'sen accordingl l I Havingthus fully describedthe nature of my invention and how the-same is to be per- I .40 ,The method of producing invisible prints-l that become visibleafBBr suitable treatment which consists in printing upon paper of any color first with a'fast'ink and-then again with j sympathetic ink, the second print. covering exactly theffirst one, and the color obtainedf fby superposing the two prints-being exactly I the same as. the color of the'paper'; substantially as and for-the purposedescribed.-

In testimonywhereofl an: iny signature 5o 1 E-RNsri-KRET's'ofiiiANN; .Witnesses'r I V VJAY.WHITE,

' L'nonoan Essen; 

